NFSv4: Fix open(O_TRUNC) and ftruncate() error handling

If the file wasn't opened for writing, then truncate and ftruncate
need to report the appropriate errors.

Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org

fs/nfs/dir.c

@@ -1429,7 +1429,7 @@ static struct dentry *nfs_atomic_lookup(struct inode *dir, struct dentry *dentry
 	}
 
 	open_flags = nd->intent.open.flags;
-	attr.ia_valid = 0;
+	attr.ia_valid = ATTR_OPEN;
 
 	ctx = create_nfs_open_context(dentry, open_flags);
 	res = ERR_CAST(ctx);
@@ -1536,7 +1536,7 @@ static int nfs_open_revalidate(struct dentry *dentry, struct nameidata *nd)
 	if (IS_ERR(ctx))
 		goto out;
 
-	attr.ia_valid = 0;
+	attr.ia_valid = ATTR_OPEN;
 	if (openflags & O_TRUNC) {
 		attr.ia_valid |= ATTR_SIZE;
 		attr.ia_size = 0;

fs/nfs/nfs4proc.c

@@ -1954,10 +1954,19 @@ static int nfs4_do_setattr(struct inode *inode, struct rpc_cred *cred,
 	};
 	int err;
 	do {
-		err = nfs4_handle_exception(server,
-				_nfs4_do_setattr(inode, cred, fattr, sattr, state),
-				&exception);
+		err = _nfs4_do_setattr(inode, cred, fattr, sattr, state);
+		switch (err) {
+		case -NFS4ERR_OPENMODE:
+			if (state && !(state->state & FMODE_WRITE)) {
+				err = -EBADF;
+				if (sattr->ia_valid & ATTR_OPEN)
+					err = -EACCES;
+				goto out;
+			}
+		}
+		err = nfs4_handle_exception(server, err, &exception);
 	} while (exception.retry);
+out:
 	return err;
 }